1. Field of the Invention
The present invention relates to prisms, and particularly, to a prism sheet used in a liquid crystal display device, and methods for making the prism sheet.
2. Discussion of the Related Art
In a liquid crystal display device (LCD device), liquid crystal is a substance that does not itself illuminate light. Instead, the liquid crystal relies on light received from a light source, in order that the liquid crystal can provide displaying of information. In the case of a typical liquid crystal display device, a backlight module powered by electricity supplies the needed light.
FIG. 6 is an exploded, side cross-sectional view of a typical liquid crystal display device 100 employing a typical prism sheet 10. The liquid crystal display device 100 includes a housing 11 and a plurality of lamps 12 positioned in the housing 11. The liquid crystal display device 100 further includes a light diffusion plate 13, a prism sheet 10, and a LCD panel 15 stacked on the housing 11 in that order. The prism sheet 10 includes a base layer 101 and a prism layer 103 formed on the base layer 101. The prism layer 103 has a plurality of prism lenses 105 having a triangular cross section. The prism lenses 105 are arranged regularly, and each extends along a direction parallel to one edge of the prism sheet 10. In use, light emitted from the lamps 12 enters the prism sheet 10 after being scattered in the diffusion plate 13. The light is refracted and concentrated by the prism lenses 105 of the prism sheet 10, and then the light finally exits the prism lenses 105 and propagates into the liquid crystal display panel 15.
Generally, a method of manufacturing the prism sheet 10 includes the following steps: First, a melted ultraviolet-cured transparent resin is coated on the base layer 101, and then the melted ultraviolet-cured transparent resin is solidified to form the prism layer 103. The prism lenses 105 formed this way can be easily damaged or scratched due to their poor rigidity and mechanical strength of the prism layer 103.
In order to protect the prism layer 103 of the prism sheet 10, the liquid crystal display device 100 usually includes an upper light diffusion film 14 disposed on the prism sheet 10. Although the upper light diffusion film 14 and the prism sheet 10 are in contact with each other, a plurality of air pockets still exist at the boundary between the light diffusion film 14 and the prism sheet 10. When the liquid crystal display device 100 is in use, light passes through the air pockets, and some of the light undergoes total reflection at one or another of the corresponding boundaries. In addition, the upper light diffusion film 14 may absorb some of the light from the prism sheet 10. As a result, a brightness of light illumination of the liquid crystal display device 100 is reduced.
Therefore, a new prism sheet and a method for making the prism sheet are desired in order to overcome the above-described shortcomings.